Glad you could join the flock!sorry to hear your duck is limping. I'm not a duck expert but from your pic it looks like it could be a case of bumble foot. It's an infection in the foot that can occur from a small cut or injury to the foot. I've not had a case my self but here is an article on it https://www.backyardchickens.com/a/bumblefoot-in-your-flock

Definatly post some pics in the emergencies section link that Mountain peeps has left for you. It may need surgery to remove it from its foot. Members there should be able to help with that or I know @TwoCrows has performed this type of thing before and should be able to help you.

Wishing you the very best of luck with your duck and hope it makes a full recovery

Looks like bumblefoot to me. You will need to cut that out of there. Get yourself some tiny instruments like any dental pics, exacto knives or scapels, tweezers, things like this and sterilize them all in boiling water for 5 mins.

Take some vet wrap that you have sliced into 1 1/2 inch thickness and some gauze. You will also need some neosprorin, without the pain killer and hydrogen peroxide. Towel up the bird with feet hanging out and lay in your lap on her back, head at your belly. There won't be much blood so don't worry about this sort of thing. You are going to only dig out that infected part. Much of that is dead and won't cause much pain. Dig, squeeze and keep digging til you get it all out. There is a core of pus in there that needs to come out. Like a zit, get that ball of pus out of there and the wound will heal. This can take 30 to 45 mins so be patient.

Once you have it all cleaned out, pour on some hydrogen peroxide and wait a moment. Then pack the hole with the neosporin. Don't stick the tip of the tube inside the hole or you will contaminate the entire tube. Use your finger and pack it well. Then put a small piece of gauze over the hole and wrap with the vet wrap. Start on the leg above the foot joint and wrap downwards toward the foot. Not too tightly, but tight enough to stay on. Wrap around the webbing and around the back of the foot. Get it wrapped well enough that no dirt is going to enter. I know that it is hard to wrap a web footed bird, but do your best. Squeeze all the vet wrap on. It has a nice stick to it that will seal nicely. After about 5 mins, feel the foot. It should be warm 5 mins later. If the foot is cold, you wrapped too tightly.

Keep this bird somewhere dry. No swimming or playing in water. Only enough water to keep the nostrils clean. Check this wound everyday for one week. If at any time it starts to look pusy, then you will need to go back in. Apply neosporin and rewrap with fresh bandages. It should have a red or dark color as it is healing. After a week or so you can check it every few days. Leave the bandage on until it is completely healed and the scab falls off. Usually about a month.